The instant patent application for the first time, describes a hydrogen storage unit useful for a hydrogen-based economy. The storage unit allows for fast and efficient cooling and/or heating thereof using gaseous hydrogen as a direct, convective heat transfer medium. The instant storage element makes it possible to efficiently and economically transfer heat between subsystems of a complete infrastructure system. Such an infrastructure system (from "source to wheel"), is the subject of copending U.S. application Ser. No. 09/444,810, entitled "A Hydrogen-based Ecosystem" filed on Nov. 22, 1999 for Ovshinsky, et al. (the '810 application), which is hereby incorporated by reference. This infrastructure, in turn, is made possible by hydrogen storage alloys that have surmounted the chemical, physical, electronic and catalytic barriers that have heretofore been considered insoluble. These alloys are fully described in copending U.S. patent application Ser. No. 09/435,497, entitled "High Storage Capacity Alloys Enabling a Hydrogen-based Ecosystem", filed on Nov. 6, 1999 for Ovshinsky et al. ("the '497 application"), which is hereby incorporated by reference. The '497 application relates generally and specifically to alloys which solve the, up to now, unanswered problem of having sufficient hydrogen storage capacity with exceptionally fast kinetics to permit the safe and efficient storage of hydrogen to provide fuel for a hydrogen based economy, such as powering internal combustion engine and fuel cell vehicles. In the '497 application the inventors for the first time disclosed the production of Mg-based alloys having both hydrogen storage capacities higher than about 6 wt. % and extraordinary kinetics. This revolutionary breakthrough was made possible by considering the materials as a system and thereby utilizing chemical modifiers and the principles of disorder and local order, pioneered by Stanford R. Ovshinsky, in such a way as to provide the necessary catalytic local order environments, such as surfaces and at the same time designing bulk characteristics for storage and high rate charge/discharge cycling. In other words, these principles allowed for tailoring of the material by controlling the particle and grain size, topology, surface states, catalytic activity, microstructure, and total interactive environments for storage capacity.
The combination of the '810 and the '497 applications solves the twin basic barriers which have held back the use of the "ultimate fuel," namely hydrogen storage capacity and a hydrogen infrastructure. With the use of the alloys of the '497 application, hydrogen can be shipped safely by boats, barges, trains, trucks, etc. when in solid form. However, the infrastructure of the '810 application requires thermal management and efficient heat utilization throughout the entire system. The instant invention makes the necessary heat transfer between the subsystems of the infrastructure simple, efficient, and economic.
As the world's population expands and its economy increases, the atmospheric concentrations of carbon dioxide are warming the earth causing climate change. However, the global energy system is moving steadily away from the carbon-rich fuels whose combustion produces the harmful gas. Experts say atmospheric levels of carbon dioxide may be double that of the pre-industrial era by the end of the next century, but they also say the levels would be much higher except for a trend toward lower-carbon fuels that has been going on for more than 100 years. Furthermore, fossil fuels cause pollution and are a causative factor in the strategic military struggles between nations. Furthermore, fluctuating energy costs are a source of economic instability worldwide
For nearly a century and a half, fuels with high amounts of carbon have progressively been replaced by those containing less. First wood, which is high in carbon, was eclipsed in the late 19th century by coal, which contains less carbon. Then oil, with a lower carbon content still, replace coal in the 1960's. Now analysts say that natural gas, lighter still in carbon, may be entering its heyday, and that the day of hydrogen--providing a fuel with no carbon at all--may at last be about to dawn. As a result, experts estimate the world's economy today burns less than two-thirds as much carbon per unit of energy produced as it did in 1860, despite the fact that carbon based fuels are still being used by the automotive industry.
In the United States, it is estimated, that the trend toward lower-carbon fuels combined with greater energy efficiency has, since 1950, reduced by about half the amount of carbon spewed out for each unit of economic production. Thus, the decarbonization of the energy system is the single most important fact to emerge from the last 20 years of analysis of the system. It had been predicted that this evolution will produce a carbon-free energy system by the end of the 21.sup.st century. The instant invention helps to shorten that period to a matter of years. In the near term, hydrogen will be used in fuel cells for cars, trucks and industrial plants, just as it already provides power for orbiting spacecraft. But ultimately, hydrogen will also provide a general carbon-free fuel to cover all fuel needs.
As noted in recent newspaper articles, large industries, especially in America, have long been suspicious of claims that the globe is warming and have vociferously negated the science of climate change. Electric utilities, among others, initially took the position that international treaties on climate change would cut economic growth and cost jobs. A dramatic shift has now occurred, in which the problems are finally being acknowledged and efforts are at last being undertaken to solve them. Therefore, it is very encouraging that some of the world's biggest companies, such as Royal Dutch/Shell and BP Amoco, two large European oil firms, now state plainly what was once considered heresy: global warming is real and merits immediate action. A number of American utilities have vowed to find ways to reduce the harm done to the atmosphere by their power plants. DuPont, the world's biggest chemical firm, has even declared that it will voluntarily reduce its emissions of greenhouse gases to 35% of their level in 1990 within a decade. The automotive industry, which is a substantial contributor to emissions of greenhouse gases and other pollutants (despite its vehicular specific reductions in emissions), has now realized that change is necessary as evidenced by their electric and hybrid vehicles. In this field, the assignee of the subject invention, has developed the Ovonic nickel metal hydride battery, the enabling battery making electric and hybrid vehicles possible.
FIG. 1, taken from reliable industrial sources, is a graph demonstrating society's move toward a carbon-free environment as a function of time starting with the use of wood in the early 1800s and ending in about 2010 with the beginning of a "hydrogen" economy. In the 1800s, fuel was primarily wood in which the ratio of hydrogen to carbon was about 0.1. As society switched to the use of coal and oil, the ratio of hydrogen to carbon increased first to 1.3 and then to 2. Currently, society is inching closer to the use of methane in which the hydrogen to carbon ratio is further increased to 4 (methane has serious problems with safety, cost and infrastructure). However, the ultimate goal for society is to employ a carbon-free fuel, i.e., the most ubiquitous of elements, pure hydrogen. The obstacle has been the lack of solid state storage capacity and infrastructure. The inventors of the '497 and the '810 applications have made this possible by inventing a 7% storage material (7% is an umoptimized figure and will be increased along with better kinetics) with exceptional absorption/desorption kinetics, i.e. at least 80% charge in less than 2 minutes and an infrastructure to use these storage alloys. These alloys allow for the first time, a safe, high capacity means of storing, transporting and delivering pure hydrogen.
Hydrogen is the "ultimate fuel." It is inexhaustible and is considered by most to be "THE" fuel for the next millennium. Hydrogen is the most plentiful element in the universe (over 95% of all matter) and was the first element created by the "Big-Bang." Hydrogen can provide a clean source of energy for our planet which can be produced by various processes which split water into hydrogen and oxygen and the hydrogen can be stored and transported in solid state form. For example, economical, lightweight, triple-junction amorphous silicon solar cells solar cells (an invention pioneered by Stanford R. Ovshinsky) such as those set forth in U.S. Pat. No. 4,678,679, (the disclosure of which is incorporated herein by reference) can be readily disposed adjacent a body of water, where their inherently high open circuit voltage can be used to dissociate water into its constituent gases, and the hydrogen so produced can be collected. These high efficiency, lightweight solar panels can also be place on nearby farms, in water, or on land. It is notable that the photovoltaic process for dissociating water to form hydrogen can be a step toward solving the problems of water purification throughout the world. Electricity can be generated to transport and pump the hydrogen into metal hydride storage beds that include the high storage capacity, lightweight metal hydride alloys. The ultra-high capacities of the alloys of the '497 application allow this hydrogen to be stored in solid form and transported by barge, tanker, train or truck in safe, economical form for ultimate use. Energy is the basic necessity of life and civilization for any society today and the use of hydrogen in the manner described herein as the basic source of energy would minimize the likelihood of wars fought for control of fossil fuels. Instead of "from well to wheel," the phrase now recited will be "from source to wheel."
In the past considerable attention has been given to the use of hydrogen as a fuel or fuel supplement. While the world's oil reserves are depletable, the supply of hydrogen remains virtually unlimited. While hydrogen can be produced from coal, natural gas and other hydrocarbons, it is preferable to form hydrogen by the electrolysis of water, preferably via energy from the sun which is composed mainly of hydrogen and can, itself, be thought of as a giant hydrogen "furnace". However, hydrogen can also be produced by the electrolysis of water using any other form of economical energy (e.g., wind, waves, geothermal, hydroelectric, nuclear, etc.) Furthermore, hydrogen, is an inherently low cost fuel. Hydrogen has the highest density of energy per unit weight of any chemical fuel and is essentially non-polluting since the main by-product of "burning" hydrogen is water. Thus, hydrogen can be a means of solving many of the world's energy related problems, such as climate change, pollution, strategic dependency on oil, etc., as well as providing a means of helping developing nations.
While hydrogen has wide potential application as a fuel, a major drawback in its utilization, especially in mobile uses such as the powering of vehicles, has been the lack of an acceptable lightweight hydrogen storage medium. Storage of hydrogen as a compressed gas involves the use of large and heavy vessels. Thus, as shown in FIG. 2, compressed hydrogen at 5000 psi only has a hydrogen density of 31 g/liter. Additionally, large and very expensive compressors are required to store hydrogen as a compressed gas and compressed hydrogen gas is a very great explosion/fire hazard.
Hydrogen also can be stored as a liquid. Storage as a liquid, however, presents a serious safety problem when used as a fuel for motor vehicles since hydrogen is extremely flammable. Liquid hydrogen also must be kept extremely cold, below -253.degree. C., and is highly volatile if spilled. Moreover, liquid hydrogen is expensive to produce and the energy necessary for the liquefaction process is a major fraction of the energy that can be generated by burning the hydrogen. Another drawback to storage as a liquid is the costly losses of hydrogen due to evaporation, which can be as high as 5% per day. Also, the storage density of liquid hydrogen, as shown in FIG. 2 is only 71 g/liter.
For the first time, storage of hydrogen as a solid hydride, using the atomically engineered alloys of the '497 application can provide a greater percent weight storage than storage as a compressed gas or a liquid in pressure tanks. Also, hydrogen storage in a solid hydride is safe and does not present any of the hazard problems that hydrogen stored in containers as a gas or a liquid does, because hydrogen, when stored in a solid hydride form, exists in it's lowest free energy state. As shown, again in FIG. 2, storage of hydrogen in a 7% Ovonic thermal hydrogen storage alloy provides a hydrogen density of 103 g/liter, more than 3 times the density of compressed hydrogen gas.
In addition to the problems associated with storage of gaseous or liquid hydrogen, there are also problems associated with the transport of hydrogen in such forms. For instance transport of liquid hydrogen will require super-insulated tanks, which will be heavy and bulky and will be susceptible to rupturing and explosion. Also, a portion of the liquid hydrogen will be required to remain in the tanks at all times to avoid heating-up and cooling down of the tank which would incur big thermal losses. As for gaseous hydrogen transportation, pressurized tankers could be used for smaller quantities of hydrogen, but these too will be susceptible to rupturing and explosion. For larger quantities, a whole new hydrogen pipeline transportation system would need to be constructed or the compressor stations, valves and gaskets of the existing pipeline systems for natural gas will have to be adapted and retrofitted to hydrogen use. This assumes, of course, that the construction material of these existing pipelines will be suited to hydrogen transportation.
The instant invention is useful in the infrastructure system of the '810 application. When hydrogen is transferred into a storage bed, heat is liberated when the hydrogen and metallic material reacts to form the hydrides. This heat must be removed to allow the hydriding reactions to proceed to completion. Conversely, heat is absorbed during the decomposition of the hydride to release hydrogen, and the hydrides are preferably heated during their decomposition to provide an adequate rate of liberation of hydrogen therefrom.
In the past, heating and cooling of the metallic hydride material has been accomplished by conventional techniques including heating or cooling the container in which the material is held, or spacing tubes throughout the bed of hydride material and circulating a heat exchange medium in the tubes. In such techniques, the amount of heat transferred to the metallic hydride depends on the area of the container or the surface area of the tubes extending through the bed, as well as on the conductive heat transfer characteristics of the metallic hydride. It has also been suggested to use hydrogen gas itself as a convective energy carrier, and, thus, overcome the limitations of the above-mentioned techniques. In addition, the direct cooling and heating of the hydrides permits rapid cycling between charge and discharge operations, and, thus, increase the efficiency of a given system. As proposed in paper number 760569 presented at the SAE Fuels and Lubricants Meeting in St. Louis, Mo., Jun. 7-10, 1976, by Hoffman et al. of Brookhaven National Laboratory, hydrogen would be circulated through the metallic hydride in the containers to carry heat directly to where it is needed. Heat exchange would take place with the hydrogen in an external heat exchanger to supply the heat to the hydrogen. This technique is also used in U.S. Pat. No. 4,185,979 issued Jan. 29, 1980 to Woolley. However, even though direct convective hydrogen cooling of the thermal hydrogen storage beds is well known in the art, no one had designed or optimized the hydrogen storage units for this type of cooling, thus there is a need for such an optimized hydrogen storage unit in the art.